1. Field of the Invention
The present invention relates to a power supply circuit for an electric device such as a television set which is provided with at least a main power supply switch and controls the operation status and the stand-by status of the electric device according to the turning ON/OFF operation of the main power supply switch and the control operation of a controlling means.
2. Description of the Related Art
Some conventional electric devices such as television sets are designed to supply the power fed from the commercial AC power source to a stand-by power supply circuit, and at the same time, to a main power supply circuit via a stand-by switch. Such an electric device usually supplies the power to a stand-by power supply circuit to make at least a controlling means, such as a microcomputer, operable so that it can be controlled by a remote control transmitter (stand-by status). To actually operate the main circuit of a device, the user manually turns on the stand-by switch or operates the power key on the remote control transmitter to turn on the stand-by switch so that the output of the main power supply circuit is supplied to the main circuit to put the device into the operation status.
FIG. 11 is a block diagram showing a power supply circuit for a conventional television set.
In FIG. 11, an AC plug 1 is connected with the commercial alternating current power source (AC), with one line of the AC plug 1 being connected with one input terminal of a first rectifier circuit 2 and the other line being connected with the other input terminal of the first rectifier circuit 2 via a switch 7-1 of a relay 7. The rectified voltage in which the commercial AC voltage is rectified and smoothed is outputted from the first rectifier circuit 2. The rectified voltage is turned into a stabilized DC voltage at a main power supply circuit 3 which is configured with a stabilized power supply circuit, such as a switching type power supply circuit, and supplied to a signal and deflection processing circuit 4 which is the main circuit of a television (TV) set. Video signals and deflection signals from the signal and deflection processing circuit 4 are supplied to a picture tube (CRT) 5.
Meanwhile, the voltage of the commercial AC power source is supplied to a primary winding 6-1 of a stand-by transformer 6, and the output voltage of a secondary winding 6-2 thereof is supplied to a second rectifier circuit 9. The rectified output voltage is supplied to a stand-by power supply circuit 10 which is configured with a stabilized power supply circuit. The output voltage Vcc of the stand-by power supply circuit 10 is supplied to a power supply input terminal 81 of a microcomputer 8 which is a controlling means. The second rectifier circuit 9 outputs a rectified voltage in which AC voltage obtained from the commercial AC power source is rectified and smoothed. The stand-by power supply circuit 10 stabilizes the rectified voltage, and at the same time, converts it into power supply voltage Vcc for microcomputer and outputs it.
Further, an output terminal of said second rectifier circuit 9 is connected with an end of a drive winding 7-2 of the relay 7 via one switch 11-1 of an interlocking switch 11, and the other end of the drive winding 7-2 is connected with an ON/OFF terminal 12 of the microcomputer 8. The interlocking switch 11 is a manually actuated main power supply switch provided with two switches 11-1 and 11-2 which are turned ON/OFF at the same time in an interlocked manner. That is, the turning on or off of one switch 11-1 is designed to be interlocked with turning on or off of the other switch 11-2. The output voltage Vcc of the stand-by power supply circuit 10 is connected with an operation (ON) instruction terminal 82 of the microcomputer 8 via the switch 11-2 in the interlocking switch 11.
With the configuration described above, in a status where the interlocking switch 11 is turned off while the commercial AC power is supplied to the AC plug 1, that is, in the stand-by status, when the interlocking switch 11 is turned on, the voltage Vcc enters a terminal 82 of the microcomputer 8 as an ON signal by turning on of the switch 11-2 of the interlocking switch 11. This causes the terminal 12 of the microcomputer 8 to be connected with a reference potential point in a device, and at the same time, turning on of the switch 11-1 lets the drive current flow from the second rectifier circuit 9 to a reference potential point via the switch 11-1, the drive winding 7-2 and the terminal 12. Consequently, the switch 7-1 of the relay is turned on and a TV set is put in the operation status. Contrarily, when the interlocking switch 11 is turned off in this operation status, the relay switch 7-1 is turned off and the TV set is put into the stand-by status again since the voltage Vcc is not supplied to the operation instruction terminal 82 of the microcomputer 8 and the power supply to the drive winding 7-2 of the relay 7 is turned off.
In order to make the TV set shown in FIG. 11 operable by a remote control transmitter 17, a light receiving circuit 83 is provided in the microcomputer 8. In case of the remote control transmitter operation, when the interlocking switch 11 is turned on to keep a TV set in the operation status, if an operation stoppage (OFF) signal is transmitted from the remote control transmitter 17, the microcomputer 8 receives and decodes this signal, and turns off the connected status (ON) of the ON/OFF terminal 12 with a reference potential point. Consequently, since the drive electric current stops flowing to the winding 7-2 of the relay 7, the switch 7-1 is turned off, putting a TV set into the stand-by status. That is, a TV set can be turned into the stand-by status by the remote control transmitter operation while the interlocking switch 11 is kept tuned on. When it is desired to return a TV set from the stand-by status caused by this remote control transmitter operation back into the operation status through the remote control transmitter operation, the user transmits an operation instruction (ON) signal from the remote control transmitter 17. This signal returns the ON/OFF terminal 12 back into the ON status with a reference potential point to turn on the relay 7, putting the TV set into the operation status. When it is desired to return a TV set from the stand-by status caused by the remote control transmitter operation back into the operation status by manual operation, the user turns off the interlocking switch 11 and turns it on again manually. Then, an operation instruction (ON) signal of voltage Vcc from the stand-by power supply circuit 10 enters into the terminal 82 of the microcomputer 8. This signal returns the terminal 12 back to the ON status to turn on the relay 7, putting the TV set into the operation status.
As described above, so long as the power from the commercial AC power source is supplied to the AC plug 1, a TV set can be put into the operation status by turning on the manual switch 11 no matter which status the TV set is in when the switch 11 is turned off, either in the operation status or in the stand-by status.
However, the configuration shown in FIG. 11 has a problem that electricity is supplied from the stand-by power supply circuit 10 to the microcomputer 8 as long as a TV set is connected with the commercial power source and electric power, even in small amount, is consumed because some power is necessary to keep the microcomputer 8 working even while the switch 11 is turned off.
There is another example of conventional electric devices such as TV sets in which electric power fed from the commercial AC power source is supplied via the main power supply switch to a power supply circuit where various power source voltages are generated. One of the power source voltage is used to keep at least a controlling means operable to stay controllable by a remote control transmitter (stand-by status), and the main circuit is turned on by operating the power key on the remote control transmitter to lead the device to the operation status when the operation of the main circuit of a device is desired.
FIG. 12 is a block diagram showing another example of a conventional TV set. The AC plug 1 is connected with the commercial alternating current power source (AC) and with the rectifier circuit 2 via a double-cut switch 13, which is the main power supply switch, and the rectified output voltage is supplied to a first power supply circuit 3 which is configured with a stabilized power supply circuit. Various power source voltages are generated from the first power supply circuit 3. The stabilized output voltage from the first power supply circuit 3 (e.g. 115 V) is supplied to a signal and deflection processing circuit 4 which is the main circuit of a TV set. Video signals and deflection signals from the signal and deflection processing circuit 4 are supplied to the picture tube (CRT) 5. Another stabilized output voltage from the first power supply circuit 3 (e.g. 5 V) is supplied to a power supply terminal 81 of the microcomputer 8 as a power supply voltage Vcc for microcomputer. Since the microcomputer 8 has been provided with the light receiving circuit 83, it can receive the infrared code signal from the remote control transmitter 17 and decode it. When the remote control transmitter 17 transmits an operation instruction (ON) signal or an operation stoppage (OFF) signal using infrared code, an ON or OFF signal is outputted from the ON/OFF terminal 12 of the microcomputer 8 and supplied to a control terminal of the signal and deflection processing circuit 4. The signal and deflection processing circuit 4 is designed to be turned into the operation status (ON) or the stand-by status (OFF) with this signal.
In the configuration shown in FIG. 12 above, when the commercial AC power source is connected with the AC plug 1 and the double-cut switch 13 is thrown in, the power supply voltage is rectified at the rectifier circuit 2 and the rectified output is stabilized at the first power supply circuit 3 and outputted. One part of the stabilized output (115 V) is supplied to a power supply terminal of the signal and deflection processing circuit 4 as a first power supply voltage, and the other part of the stabilized output voltage Vcc (5 V) is supplied as a second power supply voltage to a power supply terminal of the microcomputer 8 which is a controlling means. At this time, though the microcomputer 8 is in the status where it can operate various operation using supplied power supply voltage, the signal and deflection processing circuit 4 turns into the operation status by the circuit operation only when the ON signal is supplied to a control terminal thereof from an ON/OFF terminal 12 of the microcomputer 8. If the OFF signal is supplied from the ON/OFF terminal 12, the circuit turns into the stand-by status where the circuit operation is stopped. When the operation instruction (ON) signal is transmitted from a remote control transmitter 17, the microcomputer 8 receives this signal and outputs the ON signal from the terminal 12, putting the signal and deflection processing circuit 4 into the operation status. In order to put it into the stand-by status, the operation stoppage (OFF) instruction from the remote control transmitter 17 causes the OFF signal to be supplied from the terminal 12 of the microcomputer 8 to the signal and deflection processing circuit 4 to stop, for example, horizontal oscillation. With this, the operation of deflection circuits and high voltage circuits stops, reducing the power consumption in the main part circuit. Instead of stopping horizontal oscillation, the supply of a first power supply voltage (115 V) to the signal and deflection processing circuit 4 may be stopped.
With the configuration shown in FIG. 12, electric power is not consumed so long as a switch 13 is in the turned-off status. However, it is inconvenient that, when the switch 13 is turned off in the stand-by status of a TV set and the switch 13 is turned on again, the TV set remains in the stand-by status without turning into the operation status unless the turning on operation is done using the remote control transmitter 17 or the like. The configuration in FIG. 12 has an advantage that, when a power failure occurs and the power is restored from the power failure while a TV set is in the stand-by status, the TV set does not turn into the operation status (that is, it is dangerous and also uneconomical if, contrary to the above, a TV set starts operating without turning into the stand-by status after a power failure occurs and the power is restored from it while the set is in the stand-by status, particularly when it happens while the user is absent, leaving the TV set operating with nobody around).
As described above, a conventional television set has a problem that it consumes electric power so long as it is connected with the commercial power source, or it causes inconvenience that turning on of the main power supply switch may keep the TV set in the stand-by status, requiring the turning on operation using a remote control transmitter or the like.